Just some ideas here.

Router-Bios updated? Is it overheating?

Network cards- Checksum disabled?

Network cables- Not running through any magnetic fields? i.e. not near any power cords and such.

Crappy ISP? My provider has been notorious for blocking ports periodically and denying they did it. Also most of my trace route failures have been on my ISP's internal network.

Also, run trace routes not pings. Pings don't tell you what each hop is doing.